The present invention relates to a method of controlling an electric power steering apparatus for assisting a steering force by using an electric motor and, more particularly, to a method of controlling a motor driver using an H bridge circuit.
Vehicle convergence and hence straight driving are degraded at a high speed of 50 km/h or more for a compact automobile or 100 km/h or more for a standard automobile. In order to solve this problem, in a typical electric power steering apparatus mounted in a conventional automobile, mechanical engagement between an output shaft of an electric motor and a reduction gear is released by an electromagnetic clutch, and at the same time the electric motor is powered off. Therefore, the assisting steering force at high-speed traveling of the automobile is interrupted to improve stability or convergence of the power steering apparatus.
According to the above conventional method, however, convergence at high-speed traveling is degraded by a mechanical inertia. In particular, stability in straight traveling at the rapid start is degraded.
In order to solve the conventional problem described above, a technique is proposed to cut off the power from the electric motor of the power steering apparatus and short-circuit an armature circuit through a braking resistor when a vehicle speed exceeds a predetermined speed, thereby braking the electric motor and hence improving convergence of the power steering apparatus during high-speed traveling. This technique is disclosed in U.S. Pat. No. 4,538,698.